New Start, the landmark arms control treaty that US president Barack Obama and Russian president Dmitry Medvedev signed in Prague, represents the biggest payoff so far of Obama's reset of US-Russia relations. Lower limits for deployed nuclear warheads and delivery systems and especially the modernisation of the verification and monitoring regime contained in the original strategic arms reduction treaty (Start) are major achievements in their own right and a sign of the improved ties between Moscow and Washington.

But the renewed commitment to arms control by the US and Russia could also bolster the international diplomacy aimed at preventing Iran from obtaining a nuclear weapon.

The two nuclear superpowers' commitment to further reduce their arsenals does more than set a good example. It reinforces the legitimacy of the international nuclear non-proliferation regime and efforts to enforce it – and addressing the Iranian programme is clearly part and parcel of this system. Under article 6 of the nuclear non-proliferation treaty, the cornerstone of the global infrastructure preventing the spread of nuclear materials, countries possessing nuclear weapons like Russia and the United States are obligated "to pursue negotiations in good faith on effective measures relating to cessation of the nuclear arms race at an early date and to nuclear disarmament." With New Start, Washington and Moscow are fulfilling their obligations under the NPT.

As a result, the United States has a much better standing in negotiations over Iran's programme. Iran can no longer hide its evasions of its NPT responsibilities behind the "haves versus have-nots" red herring – the claim that nuclear states should disarm before legitimate questions about Iran's nuclear programme are answered. With the two major nuclear weapons states agreeing to reduce their arsenals Iran's refusal to come clean on its nuclear program on NPT grounds looks absurd. The New Start treaty will give the United States additional legitimacy in its attempts to pursue sanctions in the UN security council in the coming weeks.

The treaty also further consolidates the improvements in the US-Russia relationship that have occurred since Obama took office. This could increase the chances that the Russians will come on board for tougher sanctions. Indeed, Obama said today that his talks in Prague with Medvedev yielded closer co-operation on sanctions. "We cannot turn a blind eye to this," Medvedev said.

Clearly Russia will not go as far as the US or the Europeans would like, and the Kremlin will make its ultimate decision based on its understanding of Russia's national interests. But the improved climate in the relationship between Washington and Moscow that New Start puts on display is important because it decreases the chances that Russia will act as a "spoiler" just to thwart the US goals, and because it sends a signal to the Iranians that the Kremlin is in no way distancing itself from the international community on this issue.

In other words, New Start undercuts Iranian efforts to drive a wedge between Russia and the west. Historically Iran's policy shifts on its nuclear programme have correlated with upticks in US-Russia relations. Moscow is widely seen as perhaps the critical vote for a sanctions resolution, since most analysts predict that China would likely chose to abstain rather than exercise a veto – although there are some signs that even the Chinese position is softening.

The Iranians also clearly feel a bit squeezed by the Obama administration's non-proliferation agenda. Tehran is hosting its own nuclear summit called "Nuclear energy for everyone, nuclear arms for no one," a poorly disguised and almost pathetic attempt to deny Obama's nuclear security agenda the spotlight. The Iranian meeting is scheduled for 17-18 April, just days after Obama's nuclear security summit and a few weeks prior to the NPT review conference.

While New Start is a critical shot in the arm to a non-proliferation regime that has appeared faltering over the past few years, it of course does not guarantee international unanimity on Iran. Critical diplomacy with the other members of the security council, especially China and Russia, is still needed, and the outcome of the talks in New York remains unclear. Also the path to engagement should remain open if Iran decides to make a policy U-turn. But New Start could be a game changer in the international efforts to rein in Iran's nuclear ambitions.